1. Field of the Invention
The present invention relates to a reverse osmosis method of removing the salt from water in the ocean or inland bodies of salt water, using the pressure of the seawater itself, and the force of gravity.
2. Description of the Prior Art
Due to the shortage of freshwater in the southwestern United States and other arid parts of the world, there have been numerous inventions for desalinating sea water, by reverse osmosis, distillation, and other means. However, desalinization remains an expensive process. The concentrated brine produced as a by-product of desalinization can itself contribute to pollution of the environment in onshore facilities. The production of electricity or other forms of energy consumed in desalinization can also contribute to pollution of the air, water and land.
U.S. Pat. No. 3,171,808, issued on Mar. 2, 1965, to Henry W. Todd, discloses an apparatus for extracting fresh water from ocean salt water, using vanes that are not included in the present invention.
U.S. Pat. No. 3,456,802, issued on Jul. 22, 1969, to Marc Cole, discloses an apparatus for desalinization by submerged reverse osmosis, without the gravity-driven brine return of the present invention.
U.S. Pat. No. 4,125,463, issued on Nov. 14, 1978, to James W. Chenoweth, discloses a reverse osmosis desalinization apparatus and method, that is placed in a well hole for desalinating salty ground water.
U.S. Pat. No. 4,335,576, issued on Jun. 22, 1982, to Harold H. Hopfe, discloses a device for producing freshwater from seawater which floats on the surface of the sea. It derives the energy for desalinization from the motion of the waves on the surface of the water. Movement of the water on the surface causes reaction plates to move, and the movement is ultimately transmitted to pistons that move in cylinders to exert pressure on seawater to force reverse osmosis.
U.S. Pat. No. 4,452,969, issued on Jun. 5, 1984, to Fernand Lopez, discloses a reverse osmosis apparatus for producing freshwater from seawater, which is designed to be temporarily submerged, as on a fishing line. U.S. Pat. No. 4,770,775, issued on Sep. 13, 1988, to Fernand Lopez, discloses another apparatus for the production of freshwater from seawater, which is also designed to be temporarily submerged, and has a chamber that expands as freshwater is produced. Both of these apparatuses use the pressure of the seawater itself to force reverse osmosis.
U.S. Pat. No. 5,167,786, issued on Dec. 1, 1992, to William J. Eberle, discloses a wave power collection apparatus, which is anchored in the sea floor, and in one embodiment desalinates seawater by reverse osmosis. The movement of floats is used in that embodiment to turn a generator which produces electricity to power pumps that force seawater through a membrane in a reverse osmosis unit.
U.S. Pat. No. 5,229,005, issued on Jul. 20, 1993, to Yu-Si Fok and Sushil K. Gupta, discloses a process for the desalinization of seawater, by lowering reverse osmosis devices into the ocean by means of lines attached to pulleys, and raising them again by the same means to remove the freshwater produced. The pressure of the seawater itself is used to force reverse osmosis of the seawater across a membrane to produce freshwater.
U.S. Pat. No. 5,366,635, issued on Nov. 22, 1994, to Larry O. Watkins, discloses a desalinization apparatus and means in which a separator is placed on the sea floor, and the pressure at the sea floor is used to force seawater through a membrane to form freshwater by reverse osmosis, which is then pumped out.
U.S. Pat. No. 5,914,041, issued on Jun. 22, 1999, to Dennis H. Chancellor, discloses channel based reverse osmosis, in which reverse osmosis units are placed within a deep channel. The channel contains unpurified liquid (such as salt water) at a level such that the pressure across the membranes of the reverse osmosis units causes purified liquid (such as fresh water) to accumulate in cavities in the reverse osmosis units, from which it is emptied and pumped to the surface.
U.S. Pat. No. 5,916,441, issued on Jun. 29, 1999, to Roger J. Raether, discloses an apparatus for desalinating salt water in a mine shaft.
U.S. Pat. No. 5,944,999, issued on Aug. 31, 1999, to Dennis H. Chancellor, Marc Chancellor and Jacquetta M. Vogel, discloses a modular filtration system, in which the weight of the fluid being filtered is used to drive the filtration process.
British Patent No. 2,068,774, published on Aug. 19, 1981, to Jose Luis Ramo Mesple, discloses an apparatus for desalinating water by reverse osmosis in cells located deep underground, utilizing the pressure resulting from the water being deep underground.
The Osmotic Pump, by Octave Levenspiel and Noel de Nevers, Science, January 1974, Volume 183, Number 4121, pages 157-160, discloses the idea of using the weight of sea water to drive a desalinization process, but does not disclose the structures and mechanisms of the present invention.
The present invention is distinguishable from the prior art cited, in that only it takes advantage of the fact that the concentrated brine produced as a by-product of reverse osmosis desalinization is heavier than seawater to reduce the energy consumed in desalinization, by means of a gravity-driven brine return. None of the above inventions and patents, taken either singly or in combination, will be seen to describe the present invention as claimed.
The present invention is an apparatus and method of removing salt from seawater to produce potable freshwater. In the first three preferred embodiments, a large metal cylinder, with open top and bottom ends, is anchored to the floor of the ocean (or inland sea) offshore. Several pressure hulls are attached to the side of the cylinder. The interior of each pressure hull is maintained at about one atmosphere of pressure, but the hulls are submerged at a depth at which the ambient water pressure is several atmospheres. Within each pressure hull there are several reverse osmosis devices (xe2x80x9cRODsxe2x80x9d), each containing a membrane that will allow water molecules, but not sodium and chlorine ions, to pass through. Check valves allow sea water to pass from outside the hulls into the RODs. Due to the pressure differential, water molecules pass through the membranes by reverse osmosis, while salt is left behind, and freshwater is pumped out of the pressure hulls to a storage facility on shore (or where ever else it is needed). Initially, the seawater remaining on the other side of the membrane, which has a greatly increased concentration of salt due to water passing through the membrane, is pumped into the cylinder. (The water with an increased concentration of salt is hereinafter referred to as xe2x80x9cbrinexe2x80x9d.) After an initial surge, the level of the brine in the cylinder will eventually reach equilibrium, at a height below the height of the seawater outside the cylinder, due to the greater weight of the brine compared to unconcentrated seawater. After equilibrium is reached, the pumps for the brine can be turned off, as gravity will cause it to flow down from the pressure hulls through an opening near the bottom of the cylinder. This will reduce the energy needed to desalinate seawater. (It will still be necessary to pump out the freshwater.)
In the fourth preferred embodiment, a reverse osmosis system containing one or more RODs is supported by a platform on the sea floor, and there is no cylinder. In the fifth preferred embodiment, the cylinder is supported by a flotation device, and the reverse osmosis system is retained on the cylinder. In both the fourth and fifth embodiments, an elongated brine return runs downhill on the sea floor.
Accordingly, it is a principal object of the invention to provide a means for reducing the energy required to desalinate seawater. Conventional desalinization plants, located on or near the seashore, require four pumping processes: first, pumping the seawater to the plant; second, pumping to raise the pressure high enough for the RODs to operate; third, pumping the brine back out to sea; and fourth, pumping the freshwater to a reservoir or a treatment facility for further purification, and ultimately to the consumer. The present invention eliminates all but the fourth pumping process. While prior inventions of offshore desalinization apparatus, as in U.S. Pat. No. 5,366,635 to Watkins, will also eliminate the first and second processes, only the instant invention will also eliminate the third process of pumping out the brine, without requiring that energy be expended in raising the RODS, as in U.S. Pat. No. 4,452,969 to Lopez and U.S. Pat. No. 5,229,005 to Fok et al.
It is second object of the invention to provide a means for reducing the need for using expensive real estate on or near the oceanfront for desalinization facilities. As no oceanfront or near-oceanfront property is used exclusively for the process, most real estate costs associated with desalinization plants can be avoided. Some offshore site leasing may be required, but this cost should be much lower than for offshore sites involved in petroleum or mineral extraction.
It is a third object of the invention to provide a means for making the expansion of desalinization facilities easier and less expensive. As each platform must have a clear navigation zone around it (as most jurisdictions require by law), sufficient space for attaching additional pressure hulls to the cylinder will be available and facility expansion considerably eased. The expansion of a facility is limited only by the number of pressure hulls that can be fitted onto the cylinder at appropriate depths, rather than allowances made by a zoning commission with many other constituents to satisfy, as may the case with a land-based desalinization facility.
It is a fourth object of the invention is to provide a means for reducing the cost of desalinizing seawater by centralizing maintenance facilities, as the pressure hulls can be removed and taken to a central facility for maintenance, rather than the on-site maintenance required by conventional shore-based desalinization plants.
It is a fifth object of the invention to reduce pollution of the shoreline from the release of concentrated brine by desalinization plants. Conventional onshore desalinization facilities pump their brine out to sea through a bottom-laid pipeline, which releases the brine on or near the ocean floor. Releasing the brine near the ocean floor increases the area affected by the brine""s toxicity. Existing methods to reduce the toxic effects add to the cost of desalinization through greater plant infrastructure requirements or reduced process efficiency.
The present invention allows an offshore desalinization facility to release its brine into mid-water, where mixing with the ocean current is more efficient, with fewer effects upon bottom-dwelling flora and fauna. Because the facility can be located offshore, ocean currents and tidal action will thoroughly mix the brine back into the surrounding seawater, and the overall impact of increased salinity from the brine release could be infinitesimal as little as two or three kilometers down-current.
It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is cost effective, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.